In a state where a tire contacts the ground, pipe space is formed by a main groove extending in the tire circumferential direction and road surface. The rotation of tires lets air compressed in the pipe space to release outside, and as a result, air pipe resonance noise is generated. Since the air pipe resonance noise is offensive noise whose frequency is around 1 kHz, reduction in air pipe resonance noise has been demanded conventionally. For example, the pneumatic tire disclosed in Patent document 1 has a great number of oblong holes extending in the depth direction of a main groove formed in a sidewall of the main groove. Due to the oblong holes, friction resistance against the air flow in the main groove is increased, resulting in reduction of air pipe resonance noise.
Patent Document 1: Unexamined Japanese Laid-Open Patent Publication No. 10-315711(FIG. 1)